1. Field of the Invention
The present invention relates to a sensor which detects a specific component in a detection target gas.
2. Description of the Related Art
Conventionally, a gas sensor has been known which detects the concentration of a specific gas component in a detection target gas (for example, the concentration of NOx in an exhaust gas) from an internal combustion engine. In such a gas sensor, a sensing element which produces a signal corresponding to the concentration of the specific gas component, a heater which heats the sensing element, and the like are disposed. The concentration of the specific gas component is detected based on the signal which is output from the sensing element heated by the heater.
In such a gas sensor, variations between individual gas sensors may exist in the gas concentration characteristics indicating a relationship between a signal from a sensing element and the concentration of the specific gas component, and that between the resistance of a heater and the temperature of the heater.
As a sensor other than the above-described gas sensor, a soot sensor is known which detects the concentration of soot in a detection target gas. Also, in such a soot sensor, variations between individual soot sensors may exist in the characteristics indicating a relationship between a signal from a sensing element and the concentration of soot in the detection target gas.
In the NOx sensor disclosed in Patent Reference 1, to address such variations, a storage medium is provided which stores individual information indicating the gas concentration characteristics, heater temperature characteristics, and the like of the NOx sensor. A sensor control device which controls the NOx sensor is configured so that the individual information is retrieved from the storage medium, and variations among individual sensors are corrected by using the individual information, to thereby more correctly detect the NOx concentration.
[Patent Reference 1] JP-A-2011-064587
3. Problems to be Solved by the Invention
In the NOx sensor disclosed in Patent Reference 1, a circuit section 100 having the storage medium which stores the individual information of the NOx sensor is placed in a connector to which a cable from the sensor control device is connected (see FIG. 7). In the circuit section 100, a circuit board 110 on which the storage medium 111 is mounted is placed on a mount surface 121 which is located in a top portion of an output base 120, and a first circumferential side surface 122 and a second circumferential side surface 123 which extends outwards beyond the first circumferential side surface 122 are formed on the side surface of the output base 120. The entire mount surface 121 and the first circumferential side surface 122 are covered by a seal portion 130 made of a thermoplastic resin, thereby maintaining the circuit section 100 watertight.
In the NOx sensor disclosed in Patent Reference 1, however, the seal portion 130 in the circuit section 100 is placed so that the outer surface 131 of the sear portion 130 extends along the second circumferential side surface 123, and the abutment surface between the seal portion 130 and the output base 120 does not reach the second circumferential side surface 123. When the seal portion 130 contracts due to a temperature change in the circumference of the circuit section 100, therefore, there is a possibility of the seal portion 130 peeling off from the vicinity of the boundary between the first and second circumferential side surfaces 122, 123.